Many things inspire one as a composer - literature, poetry, other music. And sometimes it's painting or the visual arts, which was the case with my new piece for the Birmingham Contemporary Music Group (BCMG). The title is Ben Somewhen, and the work is a celebration of a collection of drawings of the same name by Ben Hartley, a British artist who shied away from publicity and whose simple life, devoted to his art and faith, was captured in paintings of remarkable vividness and vitality. Born in 1933, on the edge of the Peak District, he moved to Plymouth in 1960 to take up a part-time post at Plymouth College of Art. Within a year or so, he had moved to the nearby village of Ermington and the notebooks he kept in the 1960s reveal his remarkable draughtsmanship, his deep love of the local countryside and his delight in the rural community. If the drawings in the notebooks are charming in their lack of self-consciousness, the paintings transcend illustration and are concerned as much with painting itself as with figuration. He worked in gouache on brown parcel paper, taking his cue from the post-impressionists, notably Bonnard and Matisse.

The work of this fine artist has become known thanks to the initiatives of Bernard Samuels, a former director of Plymouth Arts Centre and the custodian of Hartley's work since his death in 1996. In recent years there have been regular exhibitions, and a beautifully illustrated book by Samuels was published in 2001 (Sansom & Company Ltd). The box of 104 drawings comprising Ben Somewhen was published in November 2000 in a limited edition. I was eager to buy a set as I knew these prints would have an affinity with my own idiosyncratically simple pieces.

The Ben Somewhen drawings are informed with humour and contain playful, quizzical words and phrases. The haiku-like form of these texts reminded me of some early songs using my own brief lyrics, and I remember meeting Bernard Samuels over a cup of coffee and broaching the possibility of a cycle of Ben Hartley settings. Bernard was enthusiastic and I resolved to pursue the project at an opportune moment.

Some months later, I attended a performance by the BCMG of Harrison Birtwistle's Secret Theatre, an arresting piece which plays (like Hartley's paintings, and perhaps most artistic endeavour) on the interaction of the worlds in which we live: the public and private, the real and imagined. I became absorbed in the playing of the double bassist, John Tattersdill, and distracted by the notion of a concerto in which the other musicians are sufficiently subdued to allow the bass to emerge as soloist. The mention of this idea to the BCMG's artistic director, Stephen Newbould, was enough to sow the seeds of a commission. The two proposals, the ensemble piece and the Ben Somewhen sequence, came together and it was clear from the outset it would be a perfect marriage.

And so, extraordinarily, the commission materialised. A provisional deadline was fixed, but at a convenient distance. With the double bass as protagonist, it was agreed there would be eight players in all. Tattersdill suggested the harp and I was keen to include two cellos. The result was the line-up for Ravel's Introduction and Allegro but with a second cello replacing the second violin. Plus the double bass, inevitably cast in the role of Ben Hartley, gently shepherding his fellow musicians rather than directing them.

To some extent, the process of writing Ben Somewhen was spontaneous and uncertain, although there were plenty of "clues" in the drawings. To begin with, I selected 15 of them and decided on the order. I then wrote brief descriptions of the images, using certain categories for guidance: houses and buildings; animals and birds; people; vegetation; objects and artefacts. The phrases were available, to be handled like any other text. There was always the option of a simple song without words. Or a single word could be dragooned into setting the tone. References to sounds were exploited, "a pram's squeaking song in the road" being represented by double bass harmonics (high, disembodied sounds produced by lightly touching the strings).

Hartley made the Ben Somewhen drawings using a matchstick dipped in Indian ink. They are bold and quirky but the deftness of execution and lightness of touch would disarm even the most sceptical casual observer. (No wonder that Norman Jaques, one of Hartley's first teachers, said of him: "There were other good students but none to match him for the poetry of his vision.") The certainty with which the intractable medium is handled is an inspiration. If there is hesitation here, there is no more than is necessary. There is no sense of desperation, no sense of being lost. The difficulties are invented by the artist himself and serve to galvanise and surprise.

Such confident handling of line certainly influenced my musical response. This is evident in the opening section where the melody is played in unison. The emphasis is always on definition, and on highlighting the individuality of the players. It helped that I knew the BCMG well enough to keep in mind the character of each musician. This collaboration has reminded me that composing can be a gloriously inspiring, pleasurable business.

· Birmingham Contemporary Music Group performs the premiere of Ben Somewhen by Howard Skempton at the CBSO Centre, Birmingham, on April 29, and on tour until May 29. Details: www.bcmg.org.uk